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Understanding Moisture Penetration of the Drainage Plane: a Building Science Principle Use Font Size 40 Ralph E. Moon, Ph.D. CHMM, CIAQP, MRSA GHD, Inc. [email protected] 813-971-3882 (office) 813-257-0838 (desk) Understanding Moisture Penetration of the Drainage Plane: A Building Science Principle Use Font size 40 2019 IAQA Annual Meeting Why is this relevant to the IAQ professional? • The fundamental role of any structure is to keep water out • The drainage plane constitutes the elements that protect the structure and prevent water penetration • Understanding how water penetrates a structure is necessary to identify why indoor air quality may be impaired 2019 IAQA Annual Meeting The Four Basic Rules of Water Damage • Porous materials “suck” via capillary action • Water vapor diffuses from a higher to a lower concentration gradient • Air carrying water vapor moves from high pressure to low pressure • Water runs downhill by gravity 2019 IAQA Annual Meeting Basic Rule of Water Damage No. 4 • Water runs downhill by gravity (i.e., roof and flashing leaks, attic condensation) 2019 IAQA Annual Meeting Five Forces of Rainwater Penetration • Gravity • Surface Tension • Capillary Action • Momentum (Kinetic Energy) • Air Pressure Differences 2019 IAQA Annual Meeting 2019 IAQA Annual Meeting Which forces of drainage are shown? 1. Drip 2. Stucco Cracks 3. Failed vent cover Edge Gravity Surface Tension QUIZ Capillary Action Question Momentum (Kinetic Energy) Air Pressure Differences 2019 IAQA Annual Meeting Four Strategies to Prevent Rainwater Penetration: 4 D’s • Deflection • Drainage • Drying • Durable Materials Stave Church at Urnes, Norway – Norway’s oldest stave church that dates back to the early 12th century in its present form. Wooden components of an even older church were used to build it. 2019 IAQA Annual Meeting Deflection • Deflection is the first • This part of a building principal in water system sheds water management. away from roofing and • The intent is to keep rain siding finishes, as well off the building façade as any sheathing panels and minimize penetration or water resistant of the building envelope membranes. • Pitched roofs, deep eaves or overhangs that deflect water away from the walls, proper flashing around windows and doors, and sealants applied to penetrations and joints 2019 IAQA Annual Meeting 2019 IAQA Annual Meeting What do these homes share in common? QUIZ Question 2019 IAQA Annual Meeting Outside New: Surface water drainage • Poor drainage & high water table conditions threaten slab-on-grade homes • Landscape irrigation and water reuse programs can exacerbate drainage problems • This phenomenon is known as “Damp Rising” Developer discretion 2019 IAQA Annual Meeting 2019 IAQA Annual Meeting 2019 IAQA Annual Meeting Drainage • This part of a building system sheds water away from roofing and siding finishes, as well as any sheathing panels or water resistant membranes. Diagram from J.F. Straube, Ph.D., PE • Pitched roofs, deep eaves or overhangs that deflect water away from the walls, proper flashing around windows and doors, and sealants applied to penetrations and joints 2019 IAQA Annual Meeting Wood Materials Exposed to Moisture 2019 IAQA Annual Meeting Solid Pine: Repeated Wetting and Drying 2019 IAQA Annual Meeting Exterior Grade Plywood: Repeated Wetting and Drying 2019 IAQA Annual Meeting OSB: Repeated Wetting and Drying 2019 IAQA Annual Meeting Bad Marriage Case History 5417 Owners of newly purchased home experience musty odors and respiratory irritation. Examination of home reveals no apparent plumbing leaks or water infiltration from irrigation sources. Windows reveal exterior separation of drainage plane and burglar installation methods that breach the window sill drainage plane. 2019 IAQA Annual Meeting Bad Marriage Case History 8209 Water damage and microbial growth were observed in first floor Kitchen window Water damage was beneath windows on both first and second floors Aluminum windows were positioned inset from the exterior drainage plane to give the appearance of a CMU wall Second floor windows were installed without flashing. Repair required replacement of all windows on second floor Original window installation (face 2019 IAQA Annual Meeting seal) converted to concealed barrier Paint • Moisture penetrates the exterior wall in both directions • In the heating season, water vapor moves inside to outside • In the cooling season, water vapor moves from outside to inside • When is the temperature gradient most severe? 2019 IAQA Annual Meeting Permeance Ratings* • Vapor impermeable: 0.1 perm or less (Class 1) • Vapor semi-impermeable: 1.0 perm or less and > than 0.1 perm (vapor retarder) (Class II) • Vapor semi-permeable: 10 perms or less and > 1 perm (Class III) • Vapor permeable: > than 10 perms “Perm” is a unit of measurement used to characterize permeability 2019 IAQA Annual Meeting General Classes of Permeance Impermeable Vapor semi-permeable • Rubber membranes • Plywood • Polyethylene film • Bitumen impregnated Kraft paper • Glass • OSB • Aluminum foil • Elastomeric paints • Foil-faced insulated • Most latex-based sheathing paints • Vapor semi-impermeable Permeable • Oil-based paints • Unpainted gypsum board and plaster • Vinyl wall coverings • Some latex-based paints • Housewraps 2019 IAQA Annual Meeting Caulking CAULK TYPES • Choosing the right caulk • High performance silicone requires an understanding of its • Polyurethane limitations • Polysulphide • Movement capacity is • Thermo-plastic one of the most important elastomeric factors when selecting a caulking product, • Acetoxy silicones especially if the joint • Mildew resistant moves in response to • Acrylic solar heating, changes in moisture or structural • Butyl movement • Acoustical • UV light resistance, • Oil-based compatibility, life expectancy, joint design also affect this decision2019 IAQA Annual Meeting Low Movement Caulking Medium Movement Caulking Application: Slight or infrequent joint movement Application: slow moving Types: bituminous rubber, joints i.e., masonry control oleoresinous and butyl joints rubber Types: Plasto-elastic Restrictions: should not be caulking including acrylic applied to joints in constant latex, acrylic solvent and movement cycles or large butyl and thermoplastic deflections and protected elastomerics (kreytons) from the weather Maximum Joint Movement: Maximum Joint Movement: below 25% of joint width below 5% of the joint width Service life: 5-15 years for Service life: 2-5 years when plasto-elastic and 1 used in exposed exterior 10-20 years for elasto- applications plastic material 2019 IAQA Annual Meeting Improper application of Bituminous sealant on medium To high movement joint, Orlando Mark Meshulam, Chicago Window Expert, Window Sealant Failure 2019 IAQA Annual Meeting High Movement Caulking Application: Large or fast moving joints between metals and window frames Types: One and two part polyurethanes, acetoxy and neutral cure silicones Service Life: 10-25 years 2019 IAQA Annual Meeting Caulking Use Summary Caulking Durability Application Comments Low Movement Low Suitable when low movement is Butyl rubber Caulking expected Synthetic rubber Oil based Medium High Indoor application suitable for Acrylic latex Movement small joints with limited Thermoplastic Caulking movement elastomerics High Neutral cure Movement High Suitable for indoor and outdoor silicones Caulking applications Acetoxy silicone Long service life expected Polyurethanes Polysulphides Air Leakage Control Manual, Existing Multi-Unit Residential Buildings, CMHC, 2007 2019 IAQA Annual Meeting 1. Face-Sealed Barrier Walls • Face-sealed walls are • Relatively low costs encourage face-sealed essentially impermeable to construction; however, on- water and air going maintenance will be costly • The surface is exposed to Examples extreme temperatures and • Stucco on block solar radiation that impose • EIFS stress on joints between cladding and other • Log cabins components • Sealant durability is diminished requiring regular maintenance and replacement 2019 IAQA Annual Meeting 2. Drainage Cavity Wall • Drainage cavity represents a typical brick veneer wall and many cladding systems that use stone or metal panels • Drain holes serve as vents and protect against water penetration by capillarity, surface tension and gravity • This strategy is intended to collect and control rainwater that passes through the exterior cladding 2019 IAQA Annual Meeting 3. Internal Drainage Plane Wall • This is common with stucco applications that use building paper or a non perforated building wrap as a water barrier. • A drainage screed is located at the base to increase drainage and improve drying 2019 IAQA Annual Meeting 2019 IAQA Annual Meeting Drainage Plane: Stucco Cracking • Stucco systems vary in construction sequence • 3 layer (scratch, brown, final) requires uniform application of wire mesh • Stucco must not dry too quickly • Intimate contact between the stucco and drainage plane allows penetration • Corrosive substances threaten the wire mesh in stucco Construction Skill Level 2019 IAQA Annual Meeting 4. Pressure-Equalized Rain-Screen Wall • A pressure-equalized rain screen (PER) is a drainage cavity wall that is designed so that the air pressure behind the cladding is similar to the exterior pressure. • This strategy is commonly used metal and glass curtain walls. Weeped and Pressure- 2019 IAQA Annual Meeting Vented Equalized Pressure-Equalized Rain Screen • Rainscreen systems allow air to flow into the base and out the top • Water that enters the system is removed by ventilation and by gravity down the rear face 2019 IAQA Annual
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